Inferior vena cava filters, also called IVC filters or Greenfield filters, are medical devices that are implanted into the inferior vena cava to prevent pulmonary emboli. They work by trapping emboli while still permitting the flow of blood, thereby preventing an embolus from sealing off a vessel. IVC filters are used if anticoagulation is ineffective or contraindicated.
IVC filters are inserted via the blood vessels (i.e., placed endovascularly). Known filters can be compressed into thin introducer sheaths permitting access to the venous system via the femoral vein or the internal jugular vein. An introducer sheath is guided into the IVC using fluoroscopic guidance. The filter is pushed through the introducer sheath and deployed into the desired location. IVC filters are usually positioned just below the junction of the IVC and the lowest renal vein.
A variety of different kinds of filter designs are known. Some of these are symmetrical and can be delivered through both jugular and femoral accesses. The following are some examples.
US Patent Publication No. 2003/0060843 shows a filter which has an umbrella-like structure to capture emboli with struts that connect the filter to a catheter which has a capsule on its end to hold the filter in a collapsed configuration. The catheter and capsule remain in place while the filter is in use so no vessel wall-holding features are required. The filter readily collapses as it is drawn into the capsule since there are no extensions to get in the way.
U.S. Pat. No. 6,793,665 and US Patent Publication No. 2005/0080447 show a filter with one or more meandering filaments that define a self-expanding structure that can be drawn into a catheter. The pressure of the meandering filament(s) against the vessel wall prevents the filter from migrating. In one embodiment, the filter is symmetrical and can be placed through a jugular or femoral access.
US Patent Publication No. 2005/0288703 shows a filter with a capture part with obliquely extending struts stemming from a hub which is attached at the strut endpoints to a series of V-shaped extensions that are displaced in a flow direction from the ends of the struts. The ends of the extensions have sharp tips that engage the vessel wall to prevent movement.
US Patent Publication No. 2006/0041271 shows a filter with a cover that can be placed through a catheter. The filter is self-expanding from a compressed shape that is assumed by it when it is inside the catheter. A cover over those portions of the filter that would otherwise contact the vessel wall reduces pressure on the wall. The cover also helps to resist incorporation of the filter into the vessel wall by endothelialization. Oppositely-directed tips engage the wall to prevent movement.
U.S. Pat. No. 5,370,657 shows a filter in which two self-expanding corolla elements are interlaced in opposite directions. At the center of each corolla is a hook that can be approached from opposite ends by loops that engage each hook to pull the corollas apart. The corollas are held together by a resilient element that breaks when the two corollas are pulled apart, allowing each corolla to be drawn into, and collapsed within, a sheath for retrieval.
U.S. Pat. Nos. 5,836,969 and 6,126,673 show a filter with multiple corollas that can assume a very small size when compressed within a catheter before deploying. The filter is made of filter-wires that extend generally upstream from a central region of connection, free ends that engage the vessel wall.
U.S. Pat. Nos. 6,273,901 and 6,589,266 show a filter that is similar to that of U.S. Pat. No. 5,370,657, but the wires making up the corollas follow much more complex trajectories. Also, an embodiment with hooks on the corolla hubs is shown, but they are not explained in the patent.
U.S. Pat. No. 7,018,401 shows a filter with oppositely-directed dome portions that can have hooks at the tops of their domes. The patent says the hooks can be used for retrieval. The domes are flexible.
There may be various reasons for preferring asymmetric filter designs over symmetric ones. The latter tend to be longer, for instance. It is possible the sizes of the introducer sheaths may need to be longer, depending on the particular design. Filters are generally prepackaged in the introducer sheath for at least two reasons. The first is that it is desirable for filters to be highly compressed to fit into a thin introducer sheath, which is a difficult task to perform so it is usually done under controlled conditions as a final step in manufacturing. Thus, filters are delivered pre-fitted within the introducer sheath. The second reason filters are pre-installed in the introducer sheath is for sterility. Sealed and sterilized while within the introducer sheath, the risk of contamination is greatly reduced. It is desirable for a filter of asymmetric design to be deliverable through femoral and jugular accesses without the need for separate delivery systems.